cooling fan

I have an 89 LeSabre with the 3800 v6 engine. There are 2 cooling fans for the radiator. One works all the time, and the other seems to just sit there. I do not have overheating problems, but I would like to find out what the other fan is for and why I never see it working.

I believe they come on at different temperatures. Low speed fan should come on around 200 degrees & high speed around 215. Fan shouldn't be running all the time unless the air conditioning is on.